Generally speaking, excavator buckets have on their front lip, spaced forwardly tapered spigots known as “noses” to which a tooth adaptor with a replaceable tooth is fitted.
This permits ready replacement of the teeth as they wear on a frequent basis and ready replacement of the adaptor—essentially the bulky rear portion of a tooth, on a less frequent basis.
Prior art adaptors have been retained on the bucket lip noses by frictional engagement with a large pin driven through aligned apertures in the adaptor and the nose. In some cases however, the adaptors are welded directly onto the lip as described in U.S. Pat. No. 5,709,043.
Replacement of an adaptor is effected by driving out the retaining pin to enable disengagement between the tapered spigot-like nose projection and a tapered complementary socket-like recess in the body of the adaptor. In the case of welded on adaptors, the worn adaptor must be cut from the lip with angle grinders, oxy-acetylene cutters or the like which is a very time consuming process to replace a worn adaptor.
There are however a number of disadvantages associated with prior art pinning systems in common use.
The most commonly used pinning system is known as a spool and wedge system which is inserted into aligned apertures in the nose and adaptor along an upright axis.
The spool and wedge system comprises a spool member having a tapered inner face which engages a complementary tapered face on the wedge such that relative longitudinal movement between the tapered faces causes an effective radial expansion or contraction in a plane orthogonal to the respective tapered faces.
In use, the spool member is first located in the aligned apertures of a nose and adaptor and the wedge member, with its tapered face in contact with the tapered face of the spool member, is then manually driven forcibly into the aligned apertures with a large sledgehammer having a mass of about 13 kg.
As the forces applied to a tooth/adaptor combination during excavation can be extreme and applied in many directions, it is essential to maintain a tight fit between the adaptor and nose to avoid excessive wear.
Accordingly substantial impact forces must be applied to the wedge to pull the adaptor, having a mass of several hundred kilograms, into close fitting engagement with the nose and otherwise to provide sufficient frictional force to the spool and wedge to retain the pin system in place during use.
Other devices for retaining excavator teeth on adaptors may be flex pins having two metal members separated by an elastomeric compound. When driven into aligned apertures between a tooth and an adaptor nose, the elastomeric compound is compressed against a restoring force which is said to urge the tooth into tighter engagement with the nose.
Flex pin type retention systems are subject to premature wear and deterioration in use.
Dragline maintenance staff have shown interest in alternative methods of attaching adaptors due to the high incidence of injury such as back strain, impact injuries from misdirected or glancing hammer blows and high velocity metal projectiles broken from the wedge during impact. Even after attachment, it is necessary to interrupt the operation of a dragline after some hours to tighten up the wedge.
Another significant disadvantage is the tendency to these spool and wedge pin systems to “walk” relative to each other due to large rotational moment forces applied to the adaptors during excavation. As the pins loosen, it Is common place to lose an adaptor during emptying of the excavator bucket and this necessitates immediate cessation of the excavator operation to replace the missing adaptor.
Investigations have shown that apart from the cost of replacing lost adaptor/tooth combinations a typical excavator will experience about. 24 hours down time each year at a cost of $8000-$10,000 per hour to replace lost adaptors.
Although a number of proposals for improved adaptor retention systems having been made, these have not been widely accepted.
Other prior art proposals for improved adaptor retention system are described in U.S. Pat. Nos. 5,718,070, 5,709,043, 3,196,956 and 5,423,138.
U.S. Pat. No. 5,718,070 describes an adaptor/tooth mounting arrangement wherein a wedge shaped connector pin extends through relatively large aligned apertures extending transversely in the tooth and adaptor nose. The pin is wedgingly engaged at one end and secured at its other end by a spring-loaded rotatable connector.
U.S. Pat. No. 5,423,138 describes a mounting for a tooth on an adaptor nose wherein a retaining pin extends transversely of an aperture in the nose but the free ends of the pin are located in blind recesses in the tooth by pins extending through vertical apertures in the tooth.
U.S. Pat. No. 3,196,956 also describes amounting for a tooth on an adaptor wherein a pin is located in aligned transversely extending apertures in the adaptor nose and the tooth.
U.S. Pat. No. 5,709,043 describes an adaptor having a large laterally extending recess to locate a laterally extending spring pin, a free end of which locates in one of a pair of aligned apertures in opposite sides of the tooth socket.
Other prior art tooth/adaptor mounting systems may employ aligned vertical apertures to receive a locking pin, spool and wedge, flex pin or the like.
In use the bucket lip, adaptor and tooth are subjected to a variety of load forces applied in differing directions. The greatest loads are those which apply downward rotational moment in an upright plane which moment acts to rotate the tooth/adaptor nose off the bucket lip.
A difficulty with the prior art tooth/adaptor mounting systems described above is that the horizontal or vertical apertures in the adaptor nose and the tooth tend to be relatively large to accommodate a fastening device of sufficient robustness to resist the rotational moment applied in use. These relatively large apertures reduce the cross sectional area of both the adaptor nose and the tooth socket giving rise to localised weakness with consequent breakage at these weak points.
It is an aim of the present invention to overcome or ameliorate at least some of the problems associated with the prior art tooth/adaptor mounting systems.